Effects of Nutrient and Light Limitation on Mountain Hemlock: Susceptibility to Laminated Root Rot

Abstract

Akstract: Mountain hemlock forests in the Oregon Cascades exhibit wave-form dieback resulting from mfectwn by lamm~ted root rot (Phellinus weiril). Although Phe/linus remains viable in dead ~oots a~ter the ~ave of d1eback passes, many regenerating mountain hemlock forests do not become Immediately remfected. We measured at least a doubling of nitrogen availability in the dieback and regrowth z.ones, and t~ought that this increased ~vailability could improve tree resistance to the fungus. To test this hypothesis, .we grew small mo.untam hemlocks under nutrient and light limitations in a ~o~h room, and then moculated them With the fungus. Trees growing without added nutrients had SI~~mfican~ly greater ~oha~e ~amage ~nd mortality aft~r .P_hellinus inoculation than did trees growing Wit~ nutnen~s. Shadmg sigmficantly mcreased suscept1b1hty whether or not nutrients were added. We behe:ve .that mcreased nitro~en availability and possibly increased light levels after die back in the field act sim.ilarly to mcrease resistance and prevent reinfection of the regrowing stands.Foliage damage and susceptibility to infection .were related to pool sizes of total nitrogen, phosphorus, and nonstructural carbohydrates. Plants with very low nitrogen reserves ( < 10 mg per plant), or very !.ow energy re.serves ( <~0 mg starch per plant), were more susceptible. It appears that resistance to Phellmus occurs v1a a defensive pathway that requires resources of both nutrients and carbohydrates.

Resprouting ability of Quercus crispula seedlings depends on the vegetation cover of their microhabitats

“…Low levels of carbohydrate storage may also limit resprouting success through increasing susceptibility to fungal infection. Plants with low reserves of carbohydrates show high sensitivity to infection by fungal pathogens (Wargo 1977;Carroll et al 1983;Marson and Waring 1984). In undamaged seedlings of Q. crispula growing in shaded conditions, a very important cause of mortality is dieback, probably caused by pathogenic fungal infections (Kabeya 2001), and almost all clipped seedlings that did not resprout in this study were killed by dieback.…”

Interspecific and intraspecific variation in tree seedling survival: effects of allocation to roots versus carbohydrate reserves

“…In the most general terms, carbohydrate reserves presumably play a crucial role in recovery of seedlings from a broad range of agents of stress and physical damage, ranging from herbivory to frost heaving. Carbohydrate reserves are also assumed to play a role in response to infection by pathogens (e.g., Carroll et al 1983;Matson and Waring 1984;Wargo 1972Wargo , 1977Wargo et al 1972), and in susceptibility to attack by insects (Dunn et al 1987(Dunn et al , 1990. Carbohydrate reserves also play a role in winter hardening (Sakai and Larcher 1987).…”

Biological Diversity and Terrestrial Ecosystem Biogeochemistry

“…Such systems are relatively susceptible to catastrophic die-offs of the dominant species, often but not invariably as a result of biotic agents. For example, boreal balsam fir forests are killed periodically by spruce budworm outbreaks (Holling 1981), mountain hemlock forests in the Oregon Cascades die synchronously from root rot (Matson and Waring 1984), and high altitude fir forests in Japan and the northeastern United States turn over in wave form and other diebacks (Sprugel 1976;Tadaki et al 1977;Reiners and Lang 1979). Substantial ecosystem-level biogeochemical consequences of some of these diebacks have been documented unambiguously (Sprugel 1984;Matson and Boone 1984).…”